Identification of laterally positioned servo bands employing differentiating characteristics of servo patterns

ABSTRACT

In a tape having separate servo bands of patterns positioned laterally across the tape, the patterns of a separate servo band have at least one differentiating characteristic with respect to patterns of another of the separate servo bands. The differentiating characteristic allows identification of the separate servo bands. For example, the patterns of a separate servo band have differing azimuthal orientations of detectable transitions with respect to another servo band, such as being laterally inverted. In another, variations in the width of gaps of patterns are made with respect to another servo band. In another, variations are made in the number of the detectable transitions of patterns with respect to the patterns of another servo band.

FIELD OF THE INVENTION

This invention relates to separate longitudinal servo bands which arelaterally positioned on a linear data storage tape, and, moreparticularly, to identification of the servo bands for independentaddressability.

BACKGROUND OF THE INVENTION

Linear data storage tape comprises a medium for storing large amounts ofdata, and typically comprises a plurality of data tracks that extendlongitudinally along the tape. A common example comprises magnetic tapemedia, and a less common example comprises optical tape media. A tapehead is employed for reading and/or writing data on the data tracks, andis typically shared between various data tracks or groups of datatracks, and is moved between tracks or groups of tracks in the lateraldirection of the tape. In magnetic tape media, the tape head typicallycomprises a number of separate elements which read and/or write datawith respect to a number of parallel tracks, and is provided with one ormore separate servo read transducers, which are laterally offset fromthe read and/or write elements, so as to track follow a servo band andcause the read and/or write elements of the tape head to be guided alongthe data track or tracks. In optical tape media, the optical servo maybe associated with an individual data track or a with a separate servotrack.

One type of servo system for linear data storage tape is one in whichseparate servo bands are laterally positioned on the linear data storagetape. Each of the servo bands provides the servo guidance for a group ofdata tracks, and the servo transducer of the tape head is repositionedlaterally within a servo band so the read and/or write elements accessdifferent data tracks, and is repositioned laterally to another servoband to access still further data tracks. In one example, the servobands are spaced apart and the data tracks are located between the servobands. To insure that the servoing is precise, two servo heads may beprovided at either end of the tape head, straddling the data read and/orwrite elements. The lateral positioning may be obtained from either orboth servo bands. The servo bands are encoded with essentially identicalpatterns for determining lateral position, such that the bands aresubstantially indistinguishable.

The lateral positioning of the tape head is typically accomplished byactuators, which may have mechanical or electromechanical components.Once the proper lateral positioning of the tape head has beenaccomplished, as the servo information being sensed by the servotransducer indicates, minor adjustments of the head to follow lateralmovement of the tape or of the tracks on the tape may be made. Duringtrack following, sticking or other failure of the mechanical orelectromechanical components can be ascertained from failure of thesensed servo information to show any correction. Similarly, lateralrepositioning of the tape head to different tracks within the same servoband is accomplished by a continuous adjustment of position within theservo band. Hence, any sticking or other failure of the mechanical orelectromechanical components can be ascertained by failure of the sensedservo information to show the desired movement.

However, the lateral repositioning of the head between the servo bandsis typically conducted by a coarse actuator, which may have mechanicalor electromechanical components, such as a stepper motor, and whichtypically operates in open loop without feedback. Thus, as the tape headis repositioned between the servo bands, there is no feedback from theservo information to indicate that the switch from one servo band to anyother servo band was successful, and, if the servo bands aresubstantially indistinguishable, at the supposed completion of thelateral movement, the tape head may be positioned at the wrong servoband, and the servo information will not indicate an error.

One way of determining whether the lateral movement has caused the tapehead to be positioned at the correct servo band, is to provide aseparate “independent” sensor, for example, that determines theapproximate lateral position of the head with respect to the tape. Suchan independent sensor may comprise a coarse optical sensor that measuresthe physical position of the head. Such a coarse sensor cannot be usedfor track following, but provides a backup to the actual servo system.Such extra sensors add cost to a tape drive, which is alwaysundesirable, if the extra cost can be avoided. Another example is shownby U.S. Pat. No. 6,169,640, in which timing based servo bands arelongitudinally displaced or offset from each other, such that bysimultaneously sensing two adjacent servo bands allows the servo systemto determine longitudinal offset between servo bands, from which thedata band location of the tape head can be determined. The system,however, requires that both servo bands be sensed simultaneously inorder to establish a differentiation and make a determination.

SUMMARY OF THE INVENTION

The present invention comprises, in one embodiment, a linear datastorage tape having servo information comprising a plurality of separateservo bands of patterns of detectable transitions positionedlongitudinally along the linear data storage tape, at least one of whichdetectable transitions is non-parallel to another detectable transitionin the pattern, and the separate servo bands positioned laterally acrossthe linear data storage tape; and the patterns of the separate servobands are laterally aligned, and at least one of the patterns of aseparate servo band having at least one differentiating characteristicwith respect to at least one of the laterally aligned patterns ofanother of the separate servo bands. The differentiating characteristicallows identification of the separate servo bands.

The differentiating characteristic may comprise differing azimuthalorientations of the continuously longitudinally variable detectabletransition of the laterally aligned patterns of the separate servobands. In one example, the continuously longitudinally variabledetectable transitions are inverted in the lateral direction.

Where the laterally aligned patterns comprise a plurality of gapsbetween the detectable transitions; the differentiating characteristicmay comprise variations in the gaps of the laterally aligned patterns ofthe separate servo bands, the variations in the gaps comprising at leastone expanded gap offset by at least one narrowed gap in a pattern, suchthat the separate patterns of the separate servo bands maintain thelateral alignment.

The differentiating characteristic may comprise variations in the numberof the detectable transitions of the laterally aligned patterns of theseparate servo bands. For example, where the laterally aligned patternscomprise at least one gap between the detectable transitions, thevariations in the number of the detectable transitions of the laterallyaligned patterns of the separate servo bands, may be offset bycorresponding variations in the number of the gaps, such that theseparate patterns of the separate servo bands maintain the lateralalignment.

The differentiating characteristic may comprise variations in stripewidth, comprising the longitudinal distance between sets of sequentialalternating opposite polarity detectable transitions; or may comprisereversed polarities of stripes, comprising the sets of sequentiallyalternating opposite polarity detectable transitions. Lateral alignment,if any, is independent of the variations in width or reversal ofpolarities.

Magnetic tape cartridges with the differentiating characteristic(s),servo writers, methods for providing the differentiatingcharacteristic(s), and servo readers and tape drives for reading theservo information having the differentiating characteristic(s) are alsoprovided.

If lateral alignment of the separate patterns is not necessary, in oneembodiment, where the patterns of detectable transitions are positionedlongitudinally along the linear data storage tape, the detectabletransitions comprising at least one continuously longitudinally variabledetectable transition that extends in the lateral direction of theseparate servo band, and is non-parallel to another detectabletransition in the pattern; and the separate servo bands are positionedlaterally across the linear data storage tape; at least one of thepatterns of a separate servo band has differing azimuthal orientationsof at least one continuously longitudinally variable detectabletransition with respect to at least one of the patterns of another ofthe separate servo bands. For example, the differing azimuthalorientations may comprise inverting the continuously longitudinallyvariable detectable transition in the lateral direction with respect toat least one of the patterns of another of the separate servo bands.Where at least one continuously longitudinally variable detectabletransition comprises a straight line that is slanted in the lateraldirection, the differing azimuthal orientations may comprise differingazimuthal orientations of the slant of the continuously longitudinallyvariable detectable transition with respect to at least one of thepatterns of another of the separate servo bands.

In a further embodiment, if lateral alignment of the separate patternsis not necessary, and the patterns comprise at least one gap between thenon-parallel detectable transitions; and the separate servo bands arepositioned laterally across the linear data storage tape; at least oneof the patterns of a separate servo band has variations in the gap ofthe pattern with respect to at least one of the patterns of another ofthe separate servo bands. For example, where the detectable transitionsof a pattern are arranged with at least one of the detectabletransitions in one orientation, and at least one detectable transitionin a non-parallel orientation with respect to the one orientation,having a first gap therebetween, and the patterns comprise at least asecond gap between the pattern and a sequentially adjacent pattern; andwherein the variations in the gap of the patterns of the separate servobands comprises an expanded one of the first gap and/or the second gap,and a narrowed one of the first gap and/or the second gap. In anotherexample, where the detectable transitions of a pattern are arranged in afirst burst of at least one of the detectable transitions in a firstazimuthal orientation, a second burst of at least one of the detectabletransitions in a second azimuthal orientation, a third burst of at leastone of the detectable transitions in the first azimuthal orientation,and a fourth burst of at least one of the detectable transitions in thesecond azimuthal orientation, and first gaps separating the first andthe second bursts and separating the third and the fourth bursts, andsecond gaps separating the second and the third bursts and separating asequentially adjacent pattern; and the variations in the gap of thepatterns of the separate servo bands comprises an expanded one of a setof the first gaps and a set of the second gaps and narrowed one of a setof the second gaps and a set of the first gaps. This has the same effectas though one of the servo bands was offset laterally a small amount,and added to at one side and truncated at the opposite side, such thatthe servo system can easily adjust to either band.

In another embodiment, if lateral alignment of the separate patterns isnot necessary, and the patterns comprise detectable transitionspositioned longitudinally along the linear data storage tape, at leastone of which detectable transitions is non-parallel to anotherdetectable transition in the pattern; and the separate servo bandspositioned laterally across the linear data storage tape; at least oneof the patterns of a separate servo band has variations in the number ofthe detectable transitions of the pattern with respect to at least oneof the patterns of another of the separate servo bands. Additionally,for example, where at least one of the patterns of the separate servobands comprises at least one gap between the detectable transitions, atleast one of the patterns of a separate servo band additionallycomprises variations in the number of the gaps with respect to at leastone of the patterns of another of the separate servo bands. As anotherexample, the variations in the number of the detectable transitions ofthe patterns of the separate servo bands, corresponds to the variationsin the number of the gaps. Alternatively, the patterns may additionallycomprise variations in the spacing between the detectable transitions.

Magnetic tape cartridges, servo writers, methods, and servo readers andtape drives for reading the servo information are also provided forthese embodiments.

For a fuller understanding of the present invention, reference should bemade to the following detailed description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a tape head and a segment of alinear data storage tape with a plurality of separate servo bands inaccordance with the present invention;

FIG. 2 is a representation of a servo transducer as it tracks one of theservo bands of FIG. 1, along with a representation of the servo outputsignal it generates and the corresponding signal intervals;

FIG. 3 is a representation of patterns of two separate servo bands ofFIG. 1, having an embodiment of differentiating characteristics withrespect to each other, in accordance with the present invention,comprising differing azimuthal orientations of continuouslylongitudinally variable detectable transitions of the patterns of theseparate servo bands, in which the transitions are inverted;

FIG. 4 is a representation of patterns of two separate servo bands ofFIG. 1, having an embodiment of differentiating characteristics withrespect to each other, in accordance with the present invention,comprising differing azimuthal orientations of continuouslylongitudinally variable detectable (slanted) transitions of the patternsof the separate servo bands;

FIG. 5 is a representation of patterns of two separate servo bands ofFIG. 1, having an embodiment of differentiating characteristics withrespect to each other, in accordance with the present invention,comprising variations in gaps of the patterns of the separate servobands;

FIG. 6 is a representation of patterns of two separate servo bands ofFIG. 1, having an alternate embodiment of variations in gaps of thepatterns of the separate servo bands, in accordance with the presentinvention;

FIG. 7 is a representation of patterns of two separate servo bands ofFIG. 1, having an embodiment of differentiating characteristics withrespect to each other, in accordance with the present invention,comprising variations in the number of detectable transitions of theseparate servo bands;

FIG. 8 is a representation of patterns of three separate servo bands ofFIG. 1, having an alternative embodiment of variations in the number ofdetectable transitions of the separate servo bands, in accordance withthe present invention;

FIG. 9 is a representation of patterns of three separate servo bands ofFIG. 1, having a further alternative embodiment of variations in thenumber of detectable transitions of the separate servo bands, inaccordance with the present invention;

FIG. 10 is a schematic representation of an embodiment of a magneticimprinter in accordance with the present invention, which magneticallyimprints the detectable transitions of a plurality of separate servobands on a magnetic tape media;

FIG. 11 is a schematic representation of an alternative embodiment of amagnetic imprinter in accordance with the present invention, whichmagnetically imprints the detectable transitions of a plurality ofseparate servo bands on a magnetic tape media;

FIG. 12 is an isometric representation of an embodiment of a pluralityof servo write heads for magnetically writing the detectable transitionsof a plurality of separate servo bands on a magnetic tape media;

FIG. 13 is a schematic and block representation of servo writingapparatus in accordance with the present invention, for magneticallywriting the detectable transitions of a plurality of separate servobands on a magnetic tape media;

FIG. 14 is a schematic and block representation of servo transducers anda servo reader in accordance with the present invention, for readingservo information of a plurality of separate servo bands on a magnetictape media;

FIG. 15 is a schematic representation of a magnetic tape drive employingthe servo reader of FIG. 14 and a magnetic tape media cartridgeemploying separate servo bands on magnetic tape media, in accordancewith the present invention;

FIG. 16 is a representation of two separate servo bands of FIG. 1,having an embodiment of differentiating characteristics with respect toeach other, in accordance with the present invention, comprisingvariations in stripe width; and

FIG. 17 is a representation of two separate servo bands of FIG. 1,having an embodiment of differentiating characteristics with respect toeach other, in accordance with the present invention, comprisingreversed polarities of stripes.

DETAILED DESCRIPTION OF THE INVENTION

This invention is described in preferred embodiments in the followingdescription with reference to the Figures, in which like numbersrepresent the same or similar elements. While this invention isdescribed in terms of the best mode for achieving this invention'sobjectives, it will be appreciated by those skilled in the art thatvariations may be accomplished in view of these teachings withoutdeviating from the spirit or scope of the invention.

FIGS. 1 and 2 illustrate a servo system and a linear data storage tape10, the linear data storage tape having a plurality of separatelongitudinal servo bands 11, 12, 13 and 14, which are laterallypositioned on the linear data storage tape, and which are identifiablein accordance with the present invention. The example of FIG. 1comprises a magnetic tape media with magnetically written servo bands,and with data tracks positioned between the servo bands. In magnetictape media, a tape head 16 typically comprises a number of separateelements 17, which read and/or write data with respect to a number ofparallel data tracks, and is provided with a separate servo transducer,or servo transducers 20, 21, which are laterally offset from the readand/or write elements 17, so as to track follow the servo track and beguided along the data track or tracks.

FIG. 2 illustrates a servo transducer path 25 as the servo transducertracks one of the servo bands of FIG. 1, e.g. servo band 11, along witha representation of the generated servo output signal 27 and thecorresponding signal intervals 28. The exemplary servo band is of thetype described in U.S. Pat. No. 5,689,384, which comprises patterns oftransitions recorded at more than one azimuthal orientation across thewidth of the servo band, and which are therefore non-parallel. Thetiming 28 of the signal 27 derived from reading at any point across thewidth of such a pattern varies continuously as the servo transducer 20of FIG. 1 is moved laterally across the servo track, since the servotransducer 20 is small compared to the width of the servo pattern.Lateral position sensing is achieved by deriving a ratio of two servopattern intervals A and B of FIG. 2 and therefore is insensitive to tapespeed during reading.

Referring to FIG. 1, the read and/or write elements 17 are typicallyshared between various data tracks or groups of data tracks, and ismoved between tracks or groups of tracks in the lateral direction of thetape. Each of the servo bands 11, 12, 13 and 14, provides the servoguidance for a group of data tracks, and the servo transducer 20, 21 ofthe tape head is repositioned laterally within a servo band to cause theread and/or write elements 17 to access different data tracks, and isrepositioned laterally to another servo band to access still furtherdata tracks. In one example, the servo bands are spaced apart to spanthe data tracks, which are located between the servo bands. This placesa servo band close to the corresponding data tracks to reduce the spanbetween the outer read and/or write elements and the servo band, andreduce sensitivity to changes in tape width between the time data iswritten and read back. To insure that the servoing is precise, two servotransducers 20, 21 may be provided at either end of the tape head,straddling the data read and/or write elements. The lateral positioningmay be obtained from either of the two servo bands, or by averaging orotherwise comparing data from the two servo bands.

The lateral positioning of the tape head is typically accomplished byactuators, which may have mechanical or electromechanical components.Once the proper lateral positioning of the read and/or write elements 17of the head 16 has been accomplished, as the servo information beingsensed by the servo transducer 20, 21 indicates, minor adjustments ofthe head 16 to follow lateral movement of the tape or of the tracks onthe tape may be made. During track following, sticking or other failureof the mechanical or electromechanical components can be ascertainedfrom failure of the sensed servo information to show any correction.Similarly, lateral repositioning of the tape head to different trackswithin the same servo band is accomplished by a continuous adjustment ofposition within the servo band. Hence, any sticking or other failure ofthe mechanical or electromechanical components can be ascertained byfailure of the sensed servo information to show the desired movement.

However, the lateral repositioning of the head from one of the servobands 11, 12, 13 and 14, to another, is typically conducted by a coarseactuator, which may have mechanical or electromechanical components,such as a stepper motor, and which typically operates without feedback.Thus, as the tape head is repositioned between the servo bands, there isno feedback from the servo information to indicate that the switch fromone servo band to any other servo band was successful, and, if the servobands are substantially indistinguishable, at the supposed completion ofthe lateral movement, the tape head may be positioned at the wrong servoband, and the servo information will not indicate an error.

In accordance with an aspect of the present invention, wherein theseparate servo bands 11, 12, 13 and 14, are positioned laterally acrossthe linear data storage tape; the patterns of the separate servo bandsare laterally aligned, and at least one of the patterns of a separateservo band is provided with at least one differentiating characteristicwith respect to at least one of the laterally aligned patterns ofanother of the separate servo bands. The differentiating characteristicallows identification of the separate servo bands.

The differentiating characteristic of the present invention may bestored in memory and employed to determine the servo band being sensedwithout need to simultaneously compare the two. Further, two or moreservo bands may be read if desired, not necessarily simultaneously, inorder to make the determination. Thus, alternatively, if lateralmisalignment of the separate patterns is compensated for, or alignmentis otherwise not necessary, it is not necessary that the servo bands bealigned.

FIG. 3 illustrates one type of differentiating characteristic,comprising differing azimuthal orientations of the continuouslylongitudinally variable detectable transition of the laterally alignedpatterns of the separate servo bands 31 and 32. In the example of FIG.3, the continuously longitudinally variable detectable transitions areinverted in the lateral direction. The servo band is identified byaltering the path 35 in the lateral direction and determining whetherthe “A” timing 36, e.g. between detectable transitions 37 and 38,becomes shorter or longer. For example, if the path 35 of the servotransducer is moved upwardly, toward servo band 31 while still remainingin servo band 32, the timing between detectable transitions 37 and 38becomes greater, identifying the separate servo band. If the servotransducer is instead in servo band 31, and the path of the servotransducer is moved in the same direction, upwardly, the timing betweendetectable transitions 39 and 40 becomes less, identifying the separateservo band.

Another example of differing azimuthal orientations of the continuouslylongitudinally variable detectable transition of the laterally alignedpatterns of the separate servo bands is illustrated in FIG. 4. At leastone continuously longitudinally variable detectable transition 41 ofservo band 42 comprises a straight line that is slanted in the lateraldirection, and the differentiating characteristic comprises differingazimuthal orientations of the slant of the detectable transition 41 withrespect to a continuously longitudinally variable detectable transition43 of servo band 44. The servo band is identified by altering the servotransducer path in the lateral direction and determining the rate ofchange of the “A” timing, e.g. between detectable transitions 46 and 41.For example, if the servo transducer is in servo band 44, and is movedupwardly, toward servo band 42, the timing between detectabletransitions 47 and 43 becomes greater more rapidly than if it were inservo band 42, identifying the separate servo band. If the servotransducer is instead in servo band 42, and the path of the servotransducer is moved in the same direction, upwardly, the timing betweendetectable transitions 46 and 41 becomes greater at a less rapid rate,identifying the separate servo band. Alternatively, the timing could bemeasured toward the upper edge of the separate servo band, and thetiming between detectable transitions 47 and 43 would exceed the largestpossible timing between that of detectable transitions 46 and 41,identifying the separate servo band 44. Similarly, the timing betweendetectable transitions 46 and 41 would be less than the expected timingbetween that of detectable transitions 47 and 43, identifying theseparate servo band 42.

Referring to FIGS. 1, 3 and 4, at least three separate servo bands 11,12, 13 and 14, are written on the linear data storage tape positioned insequence laterally across the linear data storage tape, such that thepatterns of the separate servo bands provide the differentiatingcharacteristic with respect to the patterns of the next separate servoband in the sequence. For example, servo bands 11 and 13 may correspondto servo band 31 of FIG. 3, and servo bands 12 and 14 of FIG. 1 maycorrespond to servo band 32 of FIG. 3. As another example, servo bands11 and 13 may correspond to servo band 42 of FIG. 4, and servo bands 12and 14 of FIG. 1 may correspond to servo band 44 of FIG. 4.

Referring to FIG. 3, the detectable transitions of a pattern of a servoband 31 may be written in a first burst 50 of at least one of thedetectable transitions in a first azimuthal orientation, a second burst51 of at least one of the detectable transitions in a second azimuthalorientation, a third burst 52 of at least one of the detectabletransitions in the first azimuthal orientation, and a fourth burst 53 ofat least one of the detectable transitions in the second azimuthalorientation; with the differing azimuthal orientations of any of thebursts of the pattern with respect to at least one of the patterns ofanother of the separate servo bands, for example, inverted in thelateral direction with respect to any or each of bursts 55, 56, 57and/or 58 of servo band 32.

In each instance, the differentiating characteristic may comprise one ormore of the patterns of the servo bands. Once the differentiatingcharacteristic is employed to identify the servo band being read by theservo transducer, the determination does not need to be repeated. Onlyif the servo transducer is moved out of a servo band, for example, toanother servo band, does the open loop character of the servo systemrequire that the newly encountered servo band be identified.

FIG. 5 illustrates another type of differentiating characteristic,comprising variations in gaps of the patterns of the separate servobands 60 and 61, where there are a plurality of gaps between thedetectable transitions. If lateral alignment of the patterns isnecessary, at least one expanded gap in a pattern is offset by at leastone narrowed gap in the pattern, such that the separate patterns of theseparate servo bands maintain the lateral alignment.

In the example of FIG. 5, the gap 63 between detectable transitions 64and 65 of servo band 60 is larger than the corresponding gap 66 betweendetectable transitions 67 and 68 of servo band 61. The servo band isidentified by determining the “A” timing, e.g. between transitions 64and 65, as compared to the “B” timing, e.g. between transitions 64 and69. The “A” timing of servo band 60 will comprise a larger share of the“B” timing, as with respect to the timing of servo band 61, where the“A” timing, e.g. between transitions 67 and 68, will comprise a smallershare of the “B” timing, e.g. between transitions 67 and 70.

Alternatively, the gap 72 between detectable transitions 65 and 69 ofservo band 60 is smaller than the corresponding gap 73 betweendetectable transitions 68 and 70 of servo band 61. The servo band isidentified by determining the “A” timing, e.g. between transitions 65and 69, as compared to the “B” timing, e.g. between transitions 64 and69. The “A” timing of servo band 60 will therefore comprise a smallershare of the “B” timing, as compared to the timing of servo band 61,where the “A” timing, e.g. between transitions 68 and 70, will comprisea larger share of the “B” timing, e.g. between transitions 67 and 70.

If lateral alignment of the servo patterns is not necessary, thevariations of gaps need not offset. Hence, some of all gaps of a servoband may be narrowed (or expanded) as compared to a separate servo band.If all gaps of a pattern or of a servo band are narrowed (or expanded),the effect is to alter the frequency of the transitions as compared to aseparate servo band. The nominal length of the pattern is also varied,changing the “A” and “B” distances of the separate servo bands.

FIG. 6 illustrates another example of variations in gaps of the patternsof the separate servo bands. In the example of FIG. 6, the detectabletransitions of a pattern 79 of servo band 80 are arranged with at leastone of the detectable transitions, e.g. of burst 81, in one orientation,and at least one detectable transition, e.g. of burst 82, in anon-parallel orientation with respect to the orientation of burst 81,having at least one first gap 83, which in the example is an expandedgap; and at least a second gap 85 between the pattern 79 and asequentially adjacent pattern 86, which in the example is a narrowedsecond gap 85. In the next servo band 87, a pattern 88 comprises a firstgap 90 between a burst 91 of at least one detectable transition andburst 92 of a least one detectable transition which is non-parallel withrespect to the orientation of burst 91, which in the example is anarrowed gap 90. At least a second gap 93 is provided between thepattern 88 and a sequentially adjacent pattern 95, which in the exampleis an expanded second gap 93. The differentiating characteristiccomprises an expanded first gap 83 of servo band 80, and a narrowedfirst gap 90 of servo band 87. Alternatively, the differentiatingcharacteristic comprises a narrowed second gap 85 of servo band 80, withrespect to the expanded second gap 93 of servo band 87. If lateralalignment of the patterns is necessary, at least one expanded gap in apattern is offset by at least one narrowed gap in the pattern, such thatthe laterally aligned separate patterns of the separate servo bandsmaintain the lateral alignment. Further, the differentiatingcharacteristic comprises the expanded first gap 83 of servo band 80,with respect to a narrowed first gap 90 of servo band 87, and thenarrowed second gap 85 of servo band 80, with respect to the expandedsecond gap 93 of servo band 87. This arrangement has the same effect asthough one of the servo bands was offset laterally a small amount, andadded to at one side and truncated at the opposite side, such that theservo system can easily adjust to either band.

The determination of the servo band being sensed is made by directlymeasuring a gap or gaps of a servo band comparing the measurement toother elements of the timing of the patterns of the servo band.Alternatively, the time of traverse between the bursts of two of theservo bands may be compared to determine which gap(s) are narrowedversus which gap(s) are expanded.

Still referring to FIG. 6, in another example, where the detectabletransitions of a pattern, e.g. pattern 100 of servo band 80, arearranged in a first burst 81 of at least one of the detectabletransitions in a first azimuthal orientation, a second burst 82 of atleast one of the detectable transitions in a second azimuthalorientation, a third burst 101 of at least one of the detectabletransitions in the first azimuthal orientation, and a fourth burst 102of at least one of the detectable transitions in the second azimuthalorientation, and first gaps 83, 103 separating the first and the secondbursts and separating the third and the fourth bursts, and second gaps85, 105 separating the second and the third bursts and separating asequentially adjacent pattern 106. The pattern 108 of the next servoband 87 has a similar arrangement, comprising a first burst 91 of atleast one of the detectable transitions in a first azimuthalorientation, a second burst 92 of at least one of the detectabletransitions in a second azimuthal orientation, a third burst 111 of atleast one of the detectable transitions in the first azimuthalorientation, and a fourth burst 112 of at least one of the detectabletransitions in the second azimuthal orientation, and first gaps 90, 113separating the first and the second bursts and separating the third andthe fourth bursts, and second gaps 93, 115 separating the second and thethird bursts and separating a sequentially adjacent pattern 116. Thevariations in the gaps of the patterns of the separate servo bandscomprises an expanded one of a set of the first gaps and/or a set of thesecond gaps and narrowed one of a set of the first gaps and/or a set ofthe second gaps.

If lateral alignment is necessary, the variations in the gaps of thepatterns of the separate servo bands comprises an expanded set of thefirst gaps and a narrowed set of the second gaps in one servo band, anda narrowed set of the first gaps and an expanded set of the second gapsin the next servo band, or vice versa, such that the laterally alignedseparate patterns maintain lateral alignment. This has the same effectas though one of the servo bands was offset laterally a small amount,and added to at one side and truncated at the opposite side, such thatthe servo system can easily adjust to either band.

As above, the determination of the servo band being sensed is made bydirectly measuring a gap or gaps of a servo band comparing themeasurement to other elements of the timing of the patterns of the servoband. Alternatively, the time of traverse between the bursts of two ofthe servo bands may be compared to determine which gap(s) are narrowedversus which gap(s) are expanded.

In each instance, the differentiating characteristic may comprise one ormore of the patterns of the servo bands. Once the differentiatingcharacteristic is employed to identify the servo band being read by theservo transducer, the determination does not need to be repeated. Onlyif the servo transducer is moved out of a servo band, for example, toanother servo band, does the open loop characteristic of the servosystem require that the newly encountered servo band be identified.

Referring to FIGS. 1, 5 and 6, at least three separate servo bands 11,12, 13 and 14, are written on the linear data storage tape positioned insequence laterally across the linear data storage tape, such that thepatterns of the separate servo bands provide the differentiatingcharacteristic with respect to the patterns of the next separate servoband in the sequence. For example, servo bands 11 and 13 may correspondto servo band 60 of FIG. 5, and servo bands 12 and 14 of FIG. 1 maycorrespond to servo band 61 of FIG. 5. As another example, servo bands11 and 13 may correspond to servo band 80 of FIG. 6, and servo bands 12and 14 of FIG. 1 may correspond to servo band 87 of FIG. 6.

FIG. 7 illustrates another differentiating characteristic, comprisingvariations in the number of detectable transitions of a pattern orpatterns of one servo band with respect to at least one of the patternsof another of the separate servo bands. In the example of FIG. 7, thenumber of detectable transitions of bursts 120 and 121 of a pattern 122of servo band 123 are different than the number of detectabletransitions of bursts 125 and 126 of pattern 127 of servo band 128. Thedetectable transitions of burst 120 are in one orientation, and thedetectable transitions of burst 121 are in a non-parallel orientationwith respect to the orientation of burst 121, and the detectabletransitions of bursts 125 and 126 are also non-parallel. If lateralalignment is necessary, variations in the width of gaps of the patternsof the separate servo bands compensate for the different numbers ofdetectable transition of the bursts. Thus, gaps 130 and 131 of servoband 123 are narrowed as compared to gaps 135 and 136 of servo band 128,such that the laterally aligned separate patterns maintain lateralalignment.

The determination of which servo band is being sensed is made bycounting the detectable transitions in the pattern. Alternatively, thenumbers of transitions in patterns of one servo band may be compared tothat of the next servo band.

Referring to FIGS. 1 and 7, at least three separate servo bands 11, 12,13 and 14, are written on the linear data storage tape positioned insequence laterally across the linear data storage tape, such that thepatterns of the separate servo bands provide the differentiatingcharacteristic with respect to the patterns of the next separate servoband in the sequence. For example, servo bands 11 and 13 may correspondto servo band 123 of FIG. 7, and servo bands 12 and 14 of FIG. 1 maycorrespond to servo band 128 of FIG. 7.

FIG. 8 illustrates another example of variations in the number ofdetectable transitions of patterns of servo bands. In FIG. 8, at leastone of the patterns 150, 151 of the separate servo bands 152, 153 havinga variation in the number of detectable transitions comprisesadditionally comprises variations in the number of the gaps with respectto at least one of the patterns of another of the separate servo bands.For example, pattern 150 of servo band 152 has gaps 160, 161 and 162,whereas pattern 151 of the next servo band 153 has gaps 165, 166, 167,168 and 169. As another example, the variations in the number of thedetectable transitions of the patterns of the separate servo bands,corresponds to the variations in the number of the gaps. If lateralalignment of the patterns of the servo bands is necessary, thevariations in the number of the detectable transitions of the laterallyaligned patterns of the separate servo bands, and variations in thenumber of the gaps, correspond, such that the laterally aligned separatepatterns of the separate servo bands maintain the lateral alignment.Thus, pattern 150 of servo band 152 comprises 18 detectable transitions,and 3 gaps, and pattern 151 of servo band 153 comprises 16 transitionsand 5 gaps.

Another way of characterizing the variations in the number of gaps andtransitions is to characterize it as stripe or transition “deletion” or“addition”.

If more than two servo bands are provided, e.g. servo bands 152, 153 and160 as illustrated in FIG. 8, they are written on the linear datastorage tape positioned in sequence laterally across the linear datastorage tape, such that the patterns of the separate servo bands providethe differentiating characteristic with respect to the patterns of thenext separate servo band in the sequence. For example, servo bands 160corresponds to servo band 152 and both are differentiated from servoband 153.

The determination of which servo band is being sensed is made bycounting the detectable transitions in the pattern, or by counting thenumber of gaps in the pattern, or by counting both. Alternatively, thenumbers of transitions and/or gaps in patterns of one servo band may becompared to that of the next servo band.

FIG. 9 illustrates still another example of variations in the number ofdetectable transitions of patterns of servo bands, and comprisesvariations in the spacing between the detectable transitions to offsetthe variations in the number of detectable transitions, such that thelaterally aligned separate patterns of the separate servo bands maintainthe lateral alignment between the patterns of the separate servo bands.In the example, pattern 170 of servo band 171 and pattern 172 of servoband 173 each comprises 18 transitions, and pattern 175 of servo band176 comprises 16 transitions, and the spacings between transitions isexpanded so that the patterns remain laterally aligned, as shown byalignments 180 and 181.

The determination of which servo band is being sensed is made bycounting the detectable transitions in the pattern. Alternatively, thenumbers of transitions in patterns of one servo band may be compared tothat of the next servo band.

Thus, in each of the above embodiments, the differentiatingcharacteristic of varying the number of detectable transitions ofpatterns of the servo bands may comprise one or more of the patterns ofthe servo bands. Once the differentiating characteristic is employed toidentify the servo band being read by the servo transducer, thedetermination does not need to be repeated. Only if the servo transduceris moved out of a servo band, for example, to another servo band, doesthe open loop character of the servo system require that the newlyencountered servo band be identified.

FIG. 16 illustrates another type of differentiating characteristics,comprising variations in stripe width. As pointed out by U.S. Pat. No.5,930,065, the “transition” of a servo system typically comprises a setof two actual transitions, a first transition having a first switch inmagnetic polarity, followed by an opposite switch in magnetic polarity.In many servo systems, only one direction of polarity switching isrecognized, ignoring the other.

Herein, the set of two actual transitions is termed a “stripe”, and isdefined as a set of sequential alternating opposite polarity detectabletransitions.

In the example of FIG. 16, the stripe width of the stripes 190 ofseparate servo band 191 are narrower in width than stripes 192 ofseparate servo band 193. The widths of the stripes are in thelongitudinal direction of the tape, and the variations are characterizedas variations in the longitudinal distance between the sequentialalternating opposite polarity detectable transitions of the sets ofdetectable transitions.

The variations are detected by detecting the timing and polarities ofthe sets of transitions, determining the sets of transitions, or leadingand trailing edges of the stripes, by the polarities of the transitions,and then determining the width of the stripes by the timing between theset of transitions. The variations are determined, for example, bycomparing the stripe widths of separate servo bands, or comparing thedistance (timing) between the transitions of a set (stripe) to thedistance (timing) between sets (stripes).

FIG. 17 illustrates still another type of differentiatingcharacteristic, comprising reversed polarities of the stripes, or setsof detectable transitions. In the example of FIG. 17, the shaded areasrepresent a magnetic field in a first direction, and the unshaded areasrepresent a magnetic field in a second direction opposite to the firstdirection. Thus, the stripes 195 of separate servo band 196 havereversed polarities with respect to the stripes 197 of separate servoband 198. The stripes 195 and 197 comprise sets of sequentialalternating opposite polarity detectable transitions.

The variations are detected by detecting the timing and polarity of thesets of transitions. In one example, the timing (distance) between thedetectable transitions of a set is different from the timing (distance)between the sets of transitions, allowing determination of the sets oftransitions. The polarities of the transitions allow determination ofwhich polarities are reversed, to identify the separate servo bands.

Lateral alignment, if any, is independent of the variations in width orreversal of polarities.

FIG. 10 illustrates an embodiment of a magnetic imprinter servo writer200 in accordance with the present invention, which magneticallyimprints the detectable transitions of a plurality of separate servobands on a magnetic tape media in accordance with methods of the presentinvention to provide differentiating characteristics with respect to theseparate servo bands. A magnetic tape 202 onto which the servo patternsare to be recorded is wound around a curved portion of the circumference204 of a drum 206 such that the curved portion is adjacent anelectromagnet 208 on the opposite side of the tape that projects amagnetic field of flux outwardly toward the tape. A sequence of raisedbands is provided on the circumference 204 of the drum in the desiredservo pattern. As is understood by those of skill in the art, the drum204 shields the magnetic tape with which the raised bands have contact,while the external electromagnet 208 projects a magnetic field onto thetape, leaving the desired servo pattern of detectable transitionsimprinted on the magnetic tape. U.S. Pat. No. 5,689,384 discusses thetechnique in more detail.

In accordance with the present invention, the sequence of raised bandsprovided on the circumference 204 of the drum 206 comprises one of thepatterns of FIG. 3 or 4, comprising differing azimuthal orientations ofthe continuously longitudinally variable detectable transitions of thelaterally aligned patterns of the separate servo bands 31 and 32 of FIG.3, or of the separate servo bands 42 and 44 of FIG. 4; or one of thepatterns of FIG. 5 or 6, comprising variations in gaps of the patternsof the separate servo bands 60 and 61 of FIG. 5, or of the separateservo bands 80 and 87 of FIG. 6; or one of the patterns of FIG. 7, 8 or9, comprising variations in the number of detectable transitions of thepatterns of the separate servo bands 123 and 128 of FIG. 7, of theseparate servo bands 152, 153 and 160 of FIG. 8, or of the separateservo bands 171, 176 and 173 of FIG. 9, or of the variations in stripewidth of separate servo bands 191 and 193 of FIG. 16, or polarityreversal of separate servo bands 196 and 198 of FIG. 17. The tape 202 ismoved longitudinally by a drive or by the drum 206 relative to the servowriter 200, and the servo writer is positioned to write two or more ofthe separate servo bands on the tape, the separate servo bandspositioned in sequence laterally across the tape; and the servo writeris operated to energize electromagnet 208 to write the separate servobands on the tape.

A result of the magnetic imprinter 200 of FIG. 10 is that the drumcontinually rotates such that the patterns of the servo bands arecontinually repeated on the magnetic tape 202. Thus, the magnetic tapeneed not be moved longitudinally significant distances to determine theservo band that is being sensed.

Another embodiment of a magnetic imprinter servo writer 220 isillustrated in FIG. 11 in accordance with the present invention, whichmagnetically imprints the detectable transitions of a plurality ofseparate servo bands on a magnetic tape media in accordance with methodsof the present invention to provide differentiating characteristics withrespect to the separate servo bands. The magnetic imprinter 220 andmethods are similar to the methods employed in the video tape industryto transfer video information from a master tape to a slave magnetictape. As is known to those of skill in the art, the prerecorded mastertape 222 has a coercivity different than that of a slave tape 223, suchthat, as the tapes are in contact on the surface of a drum 225 in thepresence of an electromagnet 228, the magnetic pattern of the mastertape 222 is imprinted on the slave tape 223.

In accordance with the present invention, at least one of the servo bandpatterns of the master tape 222 comprises one of the patterns of FIG. 3or 4, comprising differing azimuthal orientations of the continuouslylongitudinally variable detectable transitions of the laterally alignedpatterns of the separate servo bands 31 and 32 of FIG. 3, or of theseparate servo bands 42 and 44 of FIG. 4; or one of the patterns of FIG.5 or 6, comprising variations in gaps of the patterns of the separateservo bands 60 and 61 of FIG. 5, or of the separate servo bands 80 and87 of FIG. 6; or one of the patterns of FIG. 7, 8 or 9, comprisingvariations in the number of detectable transitions of the patterns ofthe separate servo bands 123 and 128 of FIG. 7, of the separate servobands 152, 153 and 160 of FIG. 8, or of the separate servo bands 171,176 and 173 of FIG. 9, or of the variations in stripe width of separateservo bands 191 and 193 of FIG. 16, or polarity reversal of separateservo bands 196 and 198 of FIG. 17. The tape 223 is moved longitudinallyrelative to the servo writer 220 by a drive or the drum 225, and theservo writer is positioned to write two or more of the separate servobands on the tape, the separate servo bands positioned in sequencelaterally across the tape; and the servo writer is operated to energizeelectromagnet 208 as master tape 222 is moved longitudinally in contactwith and at the same rate as the tape 223 to write the separate servobands on the tape 223.

The master tape 222 of FIG. 11 may be the same length as the slave tape223, such that the patterns of the servo bands may or may not repeat.Thus, the patterns of the servo bands may or may not be continuallyrepeated on the magnetic tape 223. If not repeated, the magnetic tapewill need to be moved longitudinally to the differentiatingcharacteristic portion of the tape determine the servo band that isbeing sensed.

FIGS. 12 and 13 illustrate an embodiment of servo writing apparatus inaccordance with the present invention, for magnetically writing thedetectable transitions of a plurality of separate servo bands on amagnetic tape media in accordance with methods of the present invention.The servo writer comprises a plurality of servo write heads 250, 251,252 and 253. Each of the servo write heads may also comprise separatewrite heads, or may comprise a single multi-gap write head, inaccordance with the patterns of detectable transitions to be written.

For example, if the servo patterns to be written comprise one of thepatterns of FIG. 3 or 4, comprising differing azimuthal orientations ofthe continuously longitudinally variable detectable transitions of thelaterally aligned patterns of the separate servo bands 31 and 32 of FIG.3, or of the separate servo bands 42 and 44 of FIG. 4, the servo writeheads of FIG. 12 may or may not be separate, and comprise gaps 260 and270 which are of differing azimuthal orientations at the adjacent servowrite heads in accordance with the patterns to be written. A drive movesthe tape longitudinally, and the gaps may then be pulsed simultaneouslyto record the transitions of the separate servo bands. Alternatively, ifthe servo patterns to be written one of the patterns of FIG. 5 or 6,comprising variations in gaps of the patterns of the separate servobands 60 and 61 of FIG. 5, or of the separate servo bands 80 and 87 ofFIG. 6; or one of the patterns of FIG. 7, 8 or 9, comprising variationsin the number of detectable transitions of the patterns of the separateservo bands 123 and 128 of FIG. 7, of the separate servo bands 152, 153and 160 of FIG. 8, or of the separate servo bands 171, 176 and 173 ofFIG. 9, separate write heads 280 and 285 of FIG. 12 are employed withseparate coils 290 and 295 to pulse the gaps with varied timings torecord the transitions of the separate servo bands. If the variations instripe width of the separate servo bands 191 and 193 of FIG. 16 are tobe written, coils 290 and 295 of write heads 280 and 285 of FIG. 12could be switched simultaneously, but the separate servo write heads250, 251, 252, 253 are switched at different time intervals for the setsof detectable transitions to form variations in the stripe widths. Toprovide the reversed polarity sets of detectable transitions of theseparate servo bands 196 and 198 of FIG. 17, coils 290 and 295 of writeheads 280 and 285 of FIG. 12 could be switched simultaneously, but theseparate servo write heads 250, 251, 252, 253 are switched in oppositedirections to provide the sets of detectable transitions of reversedpolarities. If the tape is D.C. biased before writing the servo bands,the separate servo bands 196 and 198 are biased at opposite polarities.An example of construction of servo write heads is provided in U.S. Pat.No. 5,689,384.

Referring additionally to FIG. 13, as a drive moves the tapelongitudinally, the servo writer is operated in accordance with thepresent invention by a servo write control 300 which operates pulsegenerators 301, 302, 303 and 304 to magnetically pulse coils 290 and 295of the servo write heads, e.g. of servo write heads 250 and 251, torecord the detectable transitions of the plurality of separate servobands on a tape 310 in at least one pattern of a sequence of a pluralityof detectable transitions positioned longitudinally along said magnetictape media, at least one of which detectable transitions is non-parallelto another of the detectable transitions in the pattern, and whichpatterns are written in accordance with methods of the present inventionto provide differentiating characteristics with respect to the separateservo bands. Thus, if the servo patterns to be written comprise one ofthe patterns of FIG. 3 or 4, comprising differing azimuthal orientationsof the continuously longitudinally variable detectable transitions ofthe laterally aligned patterns of the separate servo bands 31 and 32 ofFIG. 3, or of the separate servo bands 42 and 44 of FIG. 4, the servowrite heads of FIG. 12 comprise gaps 260 and 270 which are of differingazimuthal orientations at the adjacent servo write heads in accordancewith the patterns to be written, and the gaps 260 and 270 are pulsedsimultaneously by pulse generators 301 and 302, and by pulse generators303 and 304 to record the transitions of the separate servo bands.Alternatively, if the servo patterns to be written one of the patternsof FIG. 5 or 6, comprising variations in gaps of the patterns of theseparate servo bands 60 and 61 of FIG. 5, or of the separate servo bands80 and 87 of FIG. 6; or one of the patterns of FIG. 7, 8 or 9,comprising variations in the number of detectable transitions of thepatterns of the separate servo bands 123 and 128 of FIG. 7, of theseparate servo bands 152, 153 and 160 of FIG. 8, or of the separateservo bands 171, 176 and 173 of FIG. 9, the separate coils 290 and 295are pulsed with varied timings to record the transitions of the separateservo bands. If the variations in stripe width of the separate servobands 191 and 193 of FIG. 16 are to be written, pulse generators 301 and302 of FIG. 13 are operated at different pulse widths than pulsegenerators 303 and 304 to switch the servo write heads 250, 251, etc.,of FIG. 12 at different time intervals for the sets of detectabletransitions to form variations in the stripe widths. To provide thereversed polarity sets of detectable transitions of the separate servobands 196 and 198 of FIG. 17, pulse generators 301 and 302 of FIG. 13are operated at opposite polarities than pulse generators 303 and 304 toswitch the servo write heads 250, 251, etc., of FIG. 12 at the reversedpolarities.

FIG. 14 illustrates an embodiment of a servo reader 400 for readingservo information detected by at least one of servo transducers 401 and402 from at least one of a plurality of separate servo bands 404, 405,406 and 407 of a magnetic tape media 410. The separate servo bands arelaterally positioned on the magnetic tape media, and are identifiable inaccordance with the present invention. As discussed above, data tracksare positioned between the servo bands and read and/or written by readand/or write elements 411 of a head 416, with the separate servotransducers 401, 402 offset from the read and/or write elements, so asto track follow the servo track or tracks to guide the head along thedata tracks.

The servo bands 404, 405, 406 and 407 comprise patterns of transitionsrecorded at more than one azimuthal orientation across the width of theservo band, and which are therefore non-parallel. The timing of thesignal derived from reading at any point across the width of such apattern varies continuously as the servo transducer 401, 402 of FIG. 14is moved laterally across the servo track, since the servo transducer 20is small compared to the width of the servo pattern. Lateral positionsensing is achieved by deriving a ratio of two servo pattern intervals Aand B of FIG. 2 and therefore is insensitive to tape speed duringreading.

Each of the servo bands 404, 405, 406 and 407 provides the servoguidance for a group of data tracks, and the tape head is repositionedlaterally within a servo band to access different data tracks, and isrepositioned laterally to another servo band to access still furtherdata tracks. The lateral positioning of the tape head 416 between servobands is typically accomplished by an actuator 417, such as a steppermotor, which typically operates in open loop. Thus, as the tape head isrepositioned between the servo bands, there is no feedback from theservo information to indicate that the switch from one servo band to anyother servo band was successful, and, if the servo bands aresubstantially indistinguishable, at the supposed completion of thelateral movement, the tape head may be positioned at the wrong servoband, and the servo information will not indicate an error.

In accordance with an aspect of the present invention, wherein theseparate servo bands 404, 405, 406 and 407 are positioned laterallyacross the magnetic tape, at least one of the patterns of a separateservo band is provided with at least one differentiating characteristicwith respect to at least one of the laterally aligned patterns ofanother of the separate servo bands, the servo reader 400 employs thedifferentiating characteristic to identify the separate servo bands.

In the embodiment of FIG. 14, the detectable transitions sensed by theservo transducers 401 or 402 are detected by a corresponding servodetector 421 and 422. Either a desired one of the servo detectors 421 or422 may be operated at a time, or both may be operated simultaneously.The servo detector 421, 422 detects the timing of the detectabletransitions as sensed by the associated servo transducer 401, 402 todetermine the lateral track position of the associated servo transducerwith respect to the lateral width of the sensed separate servo band.Additionally a decoder 425 determines, from the detected transitions,which of the separate servo bands is being sensed by the transducer.

If the differentiating characteristic between the servo bands comprisesdiffering azimuthal orientations of the detectable transitions ofpatterns of the separate servo bands, as discussed with respect to FIGS.3 and 4, the servo band is identified by operating the actuator to alterthe path of the servo transducer in the lateral direction and the servodecoder 425 determines whether the “A” timing, as discussed above,becomes shorter or longer. Alternatively, the actuator is operated tomove the servo transducer toward the upper edge of the separate servoband, and the timing between detectable transitions measured todetermine whether the timing would exceed the largest possible timingbetween that of detectable transitions of the next servo band, orwhether the timing would be less than the expected timing of the nextservo band, identifying the separate servo band.

If the differentiating characteristic comprise variations in gaps of thepatterns of the separate servo bands, as in FIGS. 5 and 6, the servodecoder 425 identifies the servo band by comparing the timing betweenthe transitions to measure the width of the gaps, as discussed above, ordirectly measuring a gap or gaps of a servo band comparing themeasurement to other elements of the timing of the patterns of the servoband. Alternatively, the time of traverse between the bursts of two ofthe servo bands may be compared to determine which gap(s) are narrowedversus which gap(s) are expanded.

If the differentiating characteristic comprises variations in the numberof detectable transitions of a pattern or patterns of one servo bandwith respect to at least one of the patterns of another of the separateservo bands, the servo decoder 425 determines which servo band is beingsensed by counting the detectable transitions in the pattern.Alternatively, the numbers of transitions in patterns of one servo bandmay be compared to that of the next servo band. Still alternatively, oradditionally, if the number of gaps is also varied, the servo decoder425 may count the number of gaps in the pattern.

If the differentiating characteristic comprises the variations in stripewidth of separate servo bands 191 and 193 of FIG. 16, the servo detector421, 422 of FIG. 14 detects the polarities of the detectabletransitions. The sequence of polarities determines the sets oftransitions, or the leading and trailing edges of the stripes. The servodetectors 421, 422 also detect the timing between the transitions. Theservo decoder 425 determines the width of the stripes by the timingbetween the set of transitions. The servo decoder 425 determines thevariations in stripe width to identify the servo bands by, for example,comparing the stripe widths of separate servo bands, or comparing thedistance (timing) between the transitions of a set (stripe) to thedistance (timing) between sets (stripes).

If the differentiating characteristic comprises reversed polarities ofthe stripes of separate servo bands 196 and 198 of FIG. 17, the servodetector 421, 422 of FIG. 14 detects the polarities of the detectabletransitions. The timing of the detectable transitions determines thesets of transitions, and the decoder 425 employs the polarities of thesets of transitions to determine which polarities are reversed, toidentify the separate servo bands.

A servo control 430 operates the actuator 417 to position the magnetictape head 416 laterally with respect to the magnetic tape media 410 inaccordance with the detection of the servo detector 421, 422 and thetrack identification determination of the decoder 425.

FIG. 15 illustrates a magnetic tape drive 500 employing the servo readerof FIG. 14, and a magnetic tape media cartridge 501 having a magnetictape media 502 with separate servo bands on magnetic tape media, inaccordance with the present invention.

The magnetic tape media cartridge 501 comprises a cartridge housing 505,and a magnetic tape media 502 housed within the cartridge housing. Themagnetic tape media has servo information comprising a plurality ofseparate servo bands of at least one pattern of detectable transitionspositioned longitudinally along the magnetic tape media, at least one ofwhich detectable transitions is non-parallel to another detectabletransition in the pattern. The separate servo bands are positionedlaterally across the magnetic tape media; and at least one of thepatterns of a separate servo band has at least one differentiatingcharacteristic with respect to at least one of the patterns of anotherof the separate servo bands, as discussed above.

The magnetic tape drive 500 reads and/or writes data with respect to amagnetic tape media, such as the magnetic tape media 502 of cartridge501. The cartridge 501 is loaded into the magnetic tape drive 500 atloader 508. The magnetic tape drive 500 has a magnetic tape head, suchas head 416 of FIG. 14, and read and/or write channel for reading and/orwriting data on the magnetic tape media 502 of FIG. 15. A drivemechanism moves the magnetic tape media longitudinally with respect tothe magnetic tape head, and an actuator, such as actuator 417 of FIG.14, positions the magnetic tape head 416 laterally with respect to themagnetic tape media. At least one servo transducer narrower than thelateral width of the separate servo bands, such as servo transducers401, 402, sense the detectable transitions from at least one of theplurality of separate servo bands. A servo detector, such as servodetectors 421, 422, detects the detectable transitions as sensed by theservo transducer or transducers to determine the lateral track positionof the servo transducer with respect to the lateral width of theseparate servo bands, and the servo decoder 425 determines, from thedetected transitions, which of the separate servo bands is being sensedby the transducer, as discussed above with respect to FIG. 14, and aservo control operates an actuator to position the head accordingly.

The illustrated embodiments relate to magnetic tape servo bands, and thepresent invention may also be applied to other types of linear datastorage tape having separate servo bands, which may comprise opticaltape.

The illustrated components and/or steps may be varied, combined, orcombined functions may be separated, as is known to those of skill inthe art. The illustrated steps may be altered in sequence, omitted, orother steps added, as is known to those of skill in the art.

While the preferred embodiments of the present invention have beenillustrated in detail, it should be apparent that modifications andadaptations to those embodiments may occur to one skilled in the artwithout departing from the scope of the present invention as set forthin the following claims.

1-5. (canceled)
 6. A linear data storage tape having servo informationcomprising: a plurality of separate servo bands comprising at least onepattern of detectable transitions positioned longitudinally alone saidlinear data storage tape, at least one of which detectable transitionsis non-parallel to another detectable transition in said pattern; andsaid separate servo bands positioned laterally across said linear datastorage tape; and said patterns of said separate servo bands arelaterally aligned, and at least one of said patterns of a separate saidservo band having at least one differentiating characteristic withrespect to at least one of said laterally aligned patterns of another ofsaid separate servo bands; wherein said laterally aligned patternscomprise a plurality of gaps between said detectable transitions; andwherein said at least one differentiating characteristic comprisesvariations in said gaps of said laterally aligned patterns of saidseparate servo bands, said variations in said gaps comprise at least oneexpanded gap offset by at least one narrowed gap in a pattern, such thatsaid laterally aligned separate patterns of said separate servo bandsmaintain said lateral alignment; and wherein said detectable transitionsof a pattern are arranged with at least one of said detectabletransitions in one orientation, and at least one detectable transitionin a non-parallel orientation with respect to said one orientation,having at least one first gap therebetween, and said laterally alignedpatterns comprise at least a second gap between said pattern and asequentially adjacent pattern; and wherein said differentiatingcharacteristic comprises an expanded one of said at least one first gapand said second gap, and a narrowed one of said second gap and said atleast one first gap, such that said laterally aligned separate patternsof said separate servo bands maintain said lateral alignment.
 7. Alinear data storage tape having servo information, comprising: aplurality of separate servo bands comprising at least one pattern ofdetectable transitions positioned longitudinally along said linear datastorage tape, at least one of which detectable transitions isnon-parallel to another detectable transition in said pattern; and saidseparate servo bands positioned laterally across said linear datastorage tape; and said patterns of said separate servo bands arelaterally aligned, and at least one of said patterns of a separate saidservo band having at least one differentiating characteristic withrespect to at least one of said laterally aligned patterns of another ofsaid separate servo bands; wherein said laterally aligned patternscomprise a plurality of gaps between said detectable transitions; andwherein said at least one differentiating characteristic comprisesvariations in said gaps of said laterally aligned patterns of saidseparate servo bands, said variations in said gaps comprise at least oneexpanded gap offset by at least one narrowed gap in a pattern, such thatsaid laterally aligned separate patterns of said separate servo bandsmaintain said lateral alignment; and wherein said detectable transitionsof a pattern are arranged in a first burst of at least one of saiddetectable transitions in a first azimuthal orientation, a second burstof at least one of said detectable transitions in a second azimuthalorientation, a third burst of at least one of said detectabletransitions in said first azimuthal orientation, and a fourth burst ofat least one of said detectable transitions in said second azimuthalorientation, and first gaps separating said first and said second burstsand separating said third and said fourth bursts, and second gapsseparating said second and said third bursts and separating asequentially adjacent said pattern; and wherein said differentiatingcharacteristic comprises an expanded one of a set of said first gaps anda set of said second gaps and narrowed one of a set of said second gapsand a set of said first gaps, such that said laterally aligned separatepatterns of said separate servo bands maintain said lateral alignment.8-17. (canceled)
 18. A linear data storage tape having servoinformation, comprising: a plurality of separate servo bands comprisingat least one pattern of detectable transitions positioned longitudinallyalong said linear data storage tape, at least one of which detectabletransitions is non-parallel to another detectable transition in saidpattern; said patterns comprising at least one gap between saidnon-parallel detectable transitions; and said separate servo bandspositioned laterally across said linear data storage tape; and at leastone of said patterns of a separate said servo band having variations insaid gap of said pattern with respect to at least one of said patternsof another of said separate servo bands; wherein said detectabletransitions of a pattern are arranged with at least one of saiddetectable transitions in one orientation, and at least one detectabletransition in a non-parallel orientation with respect to said oneorientation, having a first gap therebetween, and said patterns compriseat least a second gap between said pattern and a sequentially adjacentpattern; and wherein said variations in said gap of said patterns ofsaid separate servo bands comprises an expanded one of said first gapand/or said second gap, and a narrowed one of said first gap and/or saidsecond gap.
 19. A linear data storage tape having servo information,comprising: a plurality of separate servo bands comprising at least onepattern of detectable transitions positioned longitudinally along saidlinear data storage tape, at least one of which detectable transitionsis non-parallel to another detectable transition in said pattern; saidpatterns comprising at least one gap between said non-paralleldetectable transitions; and said separate servo bands positionedlaterally across said linear data storage tape; and at least one of saidpatterns of a separate said servo band having variations in said gap ofsaid pattern with respect to at least one of said patterns of another ofsaid separate servo bands; wherein said detectable transitions of apattern are arranged in a first burst of at least one of said detectabletransitions in a first azimuthal orientation, a second burst of at leastone of said detectable transitions in a second azimuthal orientation, athird burst of at least one of said detectable transitions in said firstazimuthal orientation, and a fourth burst of at least one of saiddetectable transitions in said second azimuthal orientation, and firstgaps separating said first and said second bursts and separating saidthird and said fourth bursts, and second gaps separating said second andsaid third bursts and separating a sequentially adjacent said pattern;and wherein said variations in said gap of said patterns of saidseparate servo bands comprises an expanded one of a set of said firstgaps and/or a set of said second gaps and narrowed one of a set of saidfirst gaps and/or a set of said second gaps. 20-30. (canceled)
 31. Amethod for writing a plurality of separate servo bands on a linear datastorage tape, said separate servo bands comprising at least one patternof detectable transitions positioned longitudinally along said lineardata storage tape, at least one of which detectable transitions isnon-parallel to another detectable transition in said pattern; and saidseparate servo bands positioned laterally across said linear datastorage tape; comprising: moving said linear data storage tapelongitudinally relative to at least one servo writer, said servo writerpositioned to write a plurality of separate servo bands on said lineardata storage tape, said separate servo bands positioned laterally acrosssaid linear data storage tape; and operating said at least one servowriter to write said plurality of separate servo bands on said lineardata storage tape, each said separate servo band comprising at least onepattern of detectable transitions positioned longitudinally along saidlinear data storage tape, at least one of which detectable transitionsis non-parallel to another detectable transition in said pattern; suchthat said patterns of said separate servo bands are laterally aligned;and providing at least one differentiating characteristic of at leastone of said patterns of a separate said servo band with respect to atleast one of said laterally aligned patterns of another of said separateservo bands; wherein said laterally aligned patterns comprise aplurality of gaps between said detectable transitions; and wherein saidat least one differentiating characteristic comprises variations in saidgaps of said laterally aligned patterns of said separate servo bands,said variations in said gaps comprise at least one expanded gap offsetby at least one narrowed gap in a pattern, such that said laterallyaligned separate patterns of said separate servo bands maintain saidlateral alignment; and wherein said detectable transitions of a patternare arranged in at least one said detectable transition in oneorientation, and at least one detectable transition in a non-parallelorientation with respect to said one orientation, having a first gaptherebetween, and said laterally aligned patterns comprise at least asecond gap between said pattern and a sequentially adjacent pattern; andwherein said differentiating characteristic comprises an expanded one ofsaid first gap and said second gap, and a narrowed one of said secondgap and said first gap, such that said laterally aligned separatepatterns of said separate servo bands maintain said lateral alignment.32. A method for writing a plurality of separate servo bands on a lineardata storage tape, said separate servo bands comprising at least onepattern of detectable transitions positioned longitudinally along saidlinear data storage tape, at least one of which detectable transitionsis non-parallel to another detectable transition in said pattern; andsaid separate servo bands positioned laterally across said linear datastorage tape; comprising: moving said linear data storage tapelongitudinally relative to at least one servo writer, said servo writerpositioned to write a plurality of separate servo bands on said lineardata storage tape, said separate servo bands positioned laterally acrosssaid linear data storage tape; and operating said at least one servowriter to write said plurality of separate servo bands on said lineardata storage tape, each said separate servo band comprising at least onepattern of detectable transitions positioned longitudinally along saidlinear data storage tape, at least one of which detectable transitionsis non-parallel to another detectable transition in said pattern; suchthat said patterns of said separate servo bands are laterally aligned;and providing at least one differentiating characteristic of at leastone of said patterns of a separate said servo band with respect to atleast one of said laterally aligned patterns of another of said separateservo bands; wherein said laterally aligned patterns comprise aplurality of gaps between said detectable transitions; and wherein saidat least one differentiating characteristic comprises variations in saidgaps of said laterally aligned patterns of said separate servo bands,said variations in said gaps comprise at least one expanded gap offsetby at least one narrowed gap in a pattern, such that said laterallyaligned separate patterns of said separate servo bands maintain saidlateral alignment; and wherein said detectable transitions of a patternare arranged in a first burst of at least one of said detectabletransitions in a first azimuthal orientation, a second burst of at leastone of said detectable transitions in a second azimuthal orientation, athird burst of at least one of said detectable transitions in said firstazimuthal orientation, and a fourth burst of at least one of saiddetectable transitions in said second azimuthal orientation, and firstgaps separating said first and said second bursts and separating saidthird and said fourth bursts, and second gaps separating said second andsaid third bursts and separating a sequentially adjacent said pattern;and wherein said differentiating characteristic comprises an expandedone of a set of said first gaps and a set of said second gaps andnarrowed one of a set of said second gaps and a set of said first gaps,such that said laterally aligned separate patterns of said separateservo bands maintain said lateral alignment. 33-51. (canceled)
 52. Amethod for writing a plurality of separate servo bands on a linear datastorage tape, said separate servo bands comprising at least one patternof detectable transitions positioned longitudinally along said lineardata storage tape, at least one of which detectable transitions isnon-parallel to another detectable transition in said pattern; and saidseparate servo bands positioned laterally across said linear datastorage tape; comprising: moving said linear data storage tapelongitudinally relative to at least one servo writer, said servo writerpositioned to write a plurality of separate servo bands on said lineardata storage tape, said separate servo bands positioned laterally acrosssaid linear data storage tape; and operating said at least one servowriter to write said plurality of separate servo bands on said lineardata storage tape, each said separate servo band comprising at least onepattern of detectable transitions positioned longitudinally along saidlinear data storage tape, at least one of which detectable transitionsis non-parallel to another detectable transition in said pattern; saidpatterns comprising at least one gap between said non-paralleldetectable transitions; and providing at least one of said patterns of aseparate said servo band with variations in said gap of said patternwith respect to at least one of said patterns of another of saidseparate servo bands; wherein said detectable transitions of a patternare written with at least one of said detectable transitions in oneorientation, and at least one detectable transition in a non-parallelorientation with respect to said one orientation, having a first gaptherebetween, and said patterns comprise at least a second gap betweensaid pattern and a sequentially adjacent pattern; and wherein saidvariations in said gap of said patterns of said separate servo bandscomprises an expanded one of said first gap and/or said second gap, anda narrowed one of said first gap and/or said second gap.
 53. A methodfor writing a plurality of separate servo bands on a linear data storagetape, said separate servo bands comprising at least one pattern ofdetectable transitions positioned longitudinally along said linear datastorage tape, at least one of which detectable transitions isnon-parallel to another detectable transition in said pattern; and saidseparate servo bands positioned laterally across said linear datastorage tape; comprisng: moving said linear data storage tapelongitudinally relative to at least one servo writer, said servo writerpositioned to write a plurality of separate servo bands on said lineardata storage tape, said separate servo bands positioned laterally acrosssaid linear data storage tape; and operating said at least one servowriter to write said plurality of separate servo bands on said lineardata storage tape, each said separate servo band comprising at least onepattern of detectable transitions positioned longitudinally along saidlinear data storage tape, at least one of which detectable transitionsis non-parallel to another detectable transition in said pattern; saidpatterns comprising at least one gap between said non-paralleldetectable transitions; and providing at least one of said patterns of aseparate said servo band with variations in said gap of said patternwith respect to at least one of said patterns of another of saidseparate servo bands; wherein said detectable transitions of a patternare written in a first burst of at least one of said detectabletransitions in a first azimuthal orientation, a second burst of at leastone of said detectable transitions in a second azimuthal orientation, athird burst of at least one of said detectable transitions in said firstazimuthal orientation, and a fourth burst of at least one of saiddetectable transitions in said second azimuthal orientation, and firstgaps separating said first and said second bursts and separating saidthird and said fourth bursts, and second gaps separating said second andsaid third bursts and separating a sequentially adjacent said pattern;and wherein said variations in said gap of said patterns of saidseparate servo bands comprises an expanded one of a set of said firstgaps and/or a set of said second gaps and narrowed one of a set of saidfirst gaps and/or a set of said second gaps. 54-158. (canceled)